U.S. patent application number 09/811879 was filed with the patent office on 2002-04-18 for radio station with optimized impedance.
Invention is credited to Jagielski, Ole, Madsen, Ulrik Riis.
Application Number | 20020044100 09/811879 |
Document ID | / |
Family ID | 8168144 |
Filed Date | 2002-04-18 |
United States Patent
Application |
20020044100 |
Kind Code |
A1 |
Jagielski, Ole ; et
al. |
April 18, 2002 |
Radio station with optimized impedance
Abstract
A radio station optimizes the impedance. An antenna of a
transmitter of the radio station matches an output impedance of a
power amplifier by adding an impedance with a variable reactance. A
processor adjusts the variable reactance of the impedance according
to an output signal of the power amplifier. The impedance with the
variable reactance preferably includes either a plurality of
inductors and capacitors, variable inductors and capacitors, or a
plurality of microstrip lines. The processor calculates an optimum
value for the variable reactance according to a measurement of the
output signal of the power amplifier and stores those values for
those measured values. In this way, a table is created, so that
when the output signal is again measured the processor can use this
table to determine which variable reactance will lead to impedance
matching.
Inventors: |
Jagielski, Ole; (Aalborg,
DK) ; Madsen, Ulrik Riis; (Oak Ridge, NC) |
Correspondence
Address: |
Lerner and Greenberg PA
Post Office Box 2480
Hollywood
FL
33022-2480
US
|
Family ID: |
8168144 |
Appl. No.: |
09/811879 |
Filed: |
March 19, 2001 |
Current U.S.
Class: |
343/850 |
Current CPC
Class: |
H04B 1/04 20130101; H03H
11/485 20130101 |
Class at
Publication: |
343/850 |
International
Class: |
H01Q 001/50 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 2000 |
EP |
00 105 812.2 |
Claims
We claim:
1. A radio station for transmitting signals, the radio station
comprising: a modulator modulating a signal to be transmitted; a
power amplifier connected to said modulator for amplifying the
modulated signal and producing an output power and a test signal; a
summing device connected to said power amplifier for subtracting
the test signal of the power amplifier from a reference signal to
generate a control signal; an antenna for transmitting and
receiving the signals; an impedance with a variable reactance being
switched between said antenna and said power amplifier; an
analog-to-digital converter converting the control signal to a
digital signal; and a processor using the digital signal to change
said variable reactance of said impedance.
2. The radio station according to claim 1, wherein said processor
calculates an optimum value for the variable reactance of said
impedance according to the digital signal.
3. The radio station according to claim 2, wherein said processor
includes a table storing the optimum value for the variable
reactance of said impedance for the digital signal and relating the
stored optimum value to the respective digital signal and a
respective output power of said power amplifier.
4. The radio station according to claim 3, wherein said processor
compares the digital signal with stored values of the digital
signal to determine the reactance of said impedance.
5. The radio station according to claim 2, including: a directional
coupler transferring a first part of the output power of said power
amplifier as the test signal; a power detector connected to said
directional coupler and said summing device and receiving the first
part of the output power, said power detector converting the first
part of the output power of the power amplifier to a voltage; said
summing device subtracting the voltage from a reference voltage to
generate a difference voltage; and an integrator connected to said
summing device, receiving the difference voltage, and integrating
the difference voltage to generate the control signal and the power
amplifier generating an output power according to the control
signal.
6. The radio station according to claim 1, wherein said summing
device subtracts a supply current of said power amplifier from a
reference current to generate a difference current; and an
integrator is connected to said power amplifier for integrating the
difference current to generate the control signal; and said power
amplifier generates the output power according to the control
signal.
7. The radio station according to claim 1, wherein said power
amplifier has a gain, said analog-digital converter converts a test
voltage as the control signal of the power amplifier into the
digital signal, and said processor adjusts the gain of said power
amplifier and the variable reactance of the impedance according to
the control signal.
8. The radio station according to claim 5, wherein said impedance
includes a plurality of capacitors switched together in parallel
connected by switches of a plurality of conductors switched
together in parallel and a signal processing unit operating said
switches according to a signal from said processor.
9. The radio station according to claim 5, wherein said impedance
includes a capacitor, an inductor, and a signal processing unit for
changing a capacitance of said capacitor and an inductance of said
inductor by applying signals to said capacitor and said
inductor.
10. The radio station according to claim 5, wherein said impedance
includes a plurality of microstrip lines switched together in
parallel and a signal processing unit sending signals placed
between said microstrip lines according to a signal of said
processor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a radio station for transmitting
signals. The radio station includes a modulator modulating the
signal to be transmitted, a power amplifier amplifying the
modulated signals, a summing device subtracting a test signal of
the power amplifier for a reference signal to generate a control
signal and an antenna for transmitting and receiving the
signals.
[0003] In GSM (Global System for Mobile Communications), antennas
in mobile phones are optimized for a predefined resonance frequency
and a given frequency bandwidth.
[0004] 2. Summary of the Invention
[0005] It is accordingly an object of the invention to provide a
radio station for transmitting signals that overcomes the
hereinafore-mentioned disadvantages of the heretofore-known devices
of this general type and, in which, a change of a resonance
frequency of the antenna is minimized by adjusting an impedance
being in parallel or in series with the antenna, so that the
resonance frequency deviates only slightly from its predefined
value due to changes in the surroundings of the antenna. In this
way, the reflection characterized by the voltage standing wave
ratio (VSWR) is also minimized, so that most of the power is
transmitted. This has the advantage to saving battery life and it
also increases the life of other electrical components in the
mobile phone that do not need a large amount of reflected
power.
[0006] With the foregoing and other objects in view, there is
provided, in accordance with the invention, a radio station for
transmitting signals. The radio station includes a modulator
modulating a signal to be transmitted. A power amplifier connected
to the modulator amplifies the modulated signal and producing an
output power and a test signal. A summing device connected to the
power amplifier subtracts the test signal of the power amplifier
from a reference signal to generate a control signal. An antenna
can transmit and receive the signals. Impedance with a variable
reactance is switched between the antenna and the power amplifier.
An analog-to-digital converter converts the control signal to a
digital signal. A processor uses the digital signal to change the
variable reactance of the impedance.
[0007] In accordance with a further feature of the invention, a
processor calculates an optimum value for the impedance being
switched to the antenna according to a measurement of the output
power of a power amplifier in a transmitter of the mobile phone.
Thereby, the output power is maximized.
[0008] Furthermore, it is an advantage that the processor stores
the calculated values for each measured value, so that later, when
again the measured value is measured, the processor simply takes
the previously calculated value for the impedance in order to save
processing time.
[0009] In accordance with a further feature of the invention, a
directional coupler for transfers a part of the output power to a
power detector, so that the power detector converts the part of the
output power to a test voltage. The test voltage is used for
adjusting a power amplifier and the variable reactance.
[0010] Moreover, it is an advantage to use a current of a last
stage of the power amplifier to characterize the output power of
the power amplifier for adjusting the power amplifier and the
impedance. This is an easy solution and requires less circuit
elements.
[0011] In accordance with a further feature of the invention, a
voltage of the last stage of the power amplifier characterizes the
output power of the power amplifier. This is an easy and exact
solution to characterize the output power.
[0012] In accordance with a further feature of the invention, a
plurality of capacitors and conductors adjust by switching some of
those capacitors and inductors for the adjustment of the variable
reactance.
[0013] Alternatively, in accordance with a further feature of the
invention, the capacitors and inductors for the variable reactance
can be changed individually. In this way, the number of necessary
circuit elements for the impedance is reduced. This reduction
lowers the cost of manufacturing.
[0014] Apart from this, a further feature of the invention uses
different types of microstrip lines to provide the capacitance and
inductance of the impedance. This leads to an easy, cheap, and
straightforward implementation of the impedance.
[0015] Other features that are considered as characteristic for the
invention are set forth in the appended claims.
[0016] Although the invention is illustrated and described herein
as embodied in a radio station for transmitting signals, the
invention is nevertheless not intended to be limited to the details
shown, because various modifications and structural changes may be
made therein without departing from the spirit of the invention and
within the scope and range of equivalents of the claims.
[0017] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows a block diagram of a transmitter, a part of the
output power being transferred to a power detector;
[0019] FIG. 2 shows a block diagram of a transmitter, a current
being converted to a voltage and the voltage being used as a test
voltage;
[0020] FIG. 3 shows a block diagram of a transmitter, a voltage
being used as a test voltage;
[0021] FIG. 4 is a schematic diagram showing a circuit with
inductors and capacitors switched in parallel;
[0022] FIG. 5 is a schematic diagram showing a circuit replacing an
inductor;
[0023] FIG. 6 is a partial diagram and partial schematic view
showing a patch antenna with a switchable capacitor in series with
a shortening pin;
[0024] FIG. 7 is a view similar to FIG. 6 showing a patch antenna
with a switchable shortening pin; and
[0025] FIG. 8 is a partial schematic view similar to FIG. 6 showing
a patch antenna with a switchable capacitor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] In all the figures of the drawing, sub-features and integral
parts that correspond to one another bear the same reference symbol
in each case.
[0027] Mobile phones are constructed with constantly smaller
antennas in order to reduce the overall size of the mobile phone.
An antenna exhibits a resonance frequency being centered in a
frequency band allocated for transmitting signals by the mobile
phone. The antenna is consequently modeled by a resonance circuit
as an impedance and works as a bandpass. A smaller antenna shows a
more limited bandwidth than a larger antenna.
[0028] The impedance of the antenna is changed by objects appearing
in a vicinity of the antenna, because the objects reflect and
absorb electromagnetic energy emitted from the antenna. Examples of
such objects include a hand, different surroundings in a room, or
other people. The objects cause a changed resonance frequency of
the antenna due to the changed impedance of the antenna. The
impedance of the antenna describes the antenna itself and objects
near the antenna.
[0029] An object of the invention is to maximize the power
outputted by the amplifier in a transmitter of a mobile phone as it
transmits radio signals. When optimizing the power, the
transmission power necessary for optimizing reception by a receiver
must be considered. This means that the receiver can perform an
error-free detection of the transmitted information. To provide
this necessary transmission power, the power amplifier in the
transmitter of the mobile phone must provide that transmission
power in addition to power lost by reflections and attenuation from
the output of the power amplifier to the antenna.
[0030] If the part of the reflected power is high, then the power
amplifier must provide more output power than in the case of a
small part of reflected power. This consumes unnecessary battery
lifetime. Furthermore, the reflected power must be dissipated
somewhere, so that the electrical components in the transmitter of
the mobile phone must cope with the reflected power resulting in
unnecessary electrical and thermal stress reducing. Therefore, it
is desirable to minimize reflections due to the antenna
impedance.
[0031] In microwave electronics, however, a concept of impedance
matching is a precondition for a maximum power transfer from one
device to another device, here, from the output of the power
amplifier to the antenna. The matching condition is, that the
output impedance of the power amplifier is matched by a complex
conjugate impedance, so that all output power is transferred and
reflections of power do not occur. A measure for how much power is
reflected, is the so-called voltage standing wave ratio (VSWR). The
higher the VSWR, the more power is reflected, e.g. a VSWR of 6 to 1
means that 3 dB of the total power is reflected, that is fifty
percent (50%). A concept to keep the output power of the power
amplifier at a constant level is to apply the so called automatic
gain control (AGC). Using AGC, the output power of the power
amplifier is measured and converted to a test voltage. The test
voltage is subtracted from a reference voltage to generate a
difference voltage. The difference voltage gives a deviation of the
test voltage from the reference voltage and thereby a deviation of
the output power from the maximum amount of the output power.
Consequently, the difference voltage is a measure for the VSWR and
thereby of the impedance matching.
[0032] Referring now to the figures of the drawings in detail and
first, particularly to FIG. 1 thereof, there is shown a block
diagram of a transmitter is shown. A data source 1, most preferably
a microphone 1, with attached electronics is used to generate a
digital data stream that is then transferred to a modulator 2. The
microphone 1 converts acoustical waves into electrical signals,
whereas the attached electronics amplifies and digitizes these
electrical signals to generate the digital data stream.
Alternatively, other data sources 1 can be used: for example, a
computer, a keyboard, or a camera. The modulator 2 has a second
data input that is used to receive signals from a local oscillator
3. The local oscillator 3 generates sine waves with a certain
frequency. The digital data stream coming from the data source 1 is
used to modulate those sine waves. Here, amplitude shift keying is
used, that means a one (1) in the data streams lead to passing the
sine waves whereas a zero (0) in the data stream sets also the sine
waves to zero (0).
[0033] Alternatively, other modulation schemes can be used. In GSM,
Gaussian minimum shift keying (GMSK) is used. In GMSK, the data
bits are divided into even and odd bits and a high frequency and
low frequency signal are mapped to bit groups including an even and
an odd bit. If the odd bit is a 1 and the even bit is a 1, then a
higher frequency signal is the modulated signal. If the odd bit or
the even bit is a 1 and the corresponding odd or even bit is a -1,
then a low frequency signal is the modulated signal. If the odd bit
and the even bit are -1, then the modulated signal is again the
high frequency signal. The resulting signal is then filtered by a
Gaussian filter to make frequency transitions from the high
frequency signal to the low frequency signal and vice versa
smoother. GMSK is therefore a frequency shift keying modulation
technique.
[0034] The modulated signal is then transferred to a first input of
a power amplifier 4. The power amplifier 4 amplifies the modulated
signal according to a signal coming from an integrator 8 into a
second input of the power amplifier 4. The amplified signal is then
transferred to a coupler 5. The coupler 5 transfers a small amount
of the output power of the power amplifier 4 to a power detector
13. The larger amount (e.g. 99%) is transferred to an antenna 12
for transmitting the signals and to impedance 11 that is switched
in parallel with the antenna 12. The impedance 11 exhibits a
variable reactance in order to match the antenna impedance to the
output impedance of the coupler 5. The impedance 11 also can be
placed in series between the antenna 12 and the coupler 5.
Embodiments of the impedance are described below.
[0035] The power detector 13 includes a diode converting the
transferred power to a test voltage that is transferred to a first
input of a summing device 6. The summing device 6 has a second
input to which a reference voltage is applied, the reference
voltage coming from a voltage source 7. The difference voltage
generated by the summing device 6 is transferred to the integrator
8. The integrator 8 integrates the difference voltage in order to
generate a control signal for the power amplifier 4 and for an
analog-digital converter 9. The integrator 8 is used because an
ideal integrator has an indefinite gain for steady state signals
and consequently a real integrator has a very high gain for steady
state signals which is necessary for the stability of a loop.
[0036] The analog-digital converter 9 converts the control signal
to a digital signal. A digital signal is then transferred from the
analog-digital converter 9 to a processor 10. The processor 10
calculates for the digital signal impedance setting of the
impedance 11. This is used to match the antenna impedance to the
output impedance of the coupler 5. In this way, a maximum amount of
power is transferred to the antenna 12 for radio transmission.
[0037] In FIG. 2, a second embodiment of a transmitter after the
invention is shown. A data source 14, which is, as mentioned above
a microphone with an attached electronics is connected to a first
input of a modulator 16. The modulator 16 has a second input that
is used for receiving signals from a local oscillator 15. The
modulated signal is then transferred from the modulator 16 to a
first input of a power amplifier 17. The power amplifier 17
amplifies the modulated signal according to a control signal from
an integrator 19. The amplified signal is then transferred to an
antenna 24 and impedance 23 which is switched in parallel to the
antenna 24. The impedance 23 is used to match the impedance of the
antenna 24 to the output impedance of the power amplifier 17.
Alternatively, the impedance 23 can be switched in series between
the power amplifier 17 and the antenna 24.
[0038] From the power amplifier 17, an output is connected to a
summing device 18. This data output transfers a current of the last
stage of the power amplifier 17 to the summing device 18. In the
summing device 18, this current is converted to a test voltage.
Then, the summing device 18 subtracts this test voltage from a
reference voltage, the reference voltage being generated by a
voltage source 22. The difference of the test voltage and the
reference voltage is then transferred to the integrator 19, which
integrates the difference voltage. The output of the integrator 19
is connected to a second input of the power amplifier 17 and to an
analog-digital converter 20. The analog-digital converter 20
converts the control signal of the integrator into a digital
signal. The digital signal is then transferred from the
analog-digital converter 20 to a processor 21. The processor 21
calculates for the digital signal an optimum impedance setting for
the impedance 23. A signal is then transferred from the processor
21 to the impedance 23. The impedance 23 exhibits a signal
processing unit that is used for setting a variable reactance of
the impedance 23. Alternatively, the processor 21 sets the
impedance 23 directly.
[0039] In FIG. 3, a third embodiment of the invention is shown. A
data source 25 generates a digital data stream that is transferred
to a modulator 27 modulating the digital data stream on a signal
containing of single frequency sine waves coming from a local
oscillator 26. The modulated signal is then transferred from the
modulator 27 to a power amplifier 28. The power amplifier 28
amplifies the modulated signal according to a control signal coming
from a processor 30. The amplified signal is then transferred from
a first output of the power amplifier 28 to an antenna 32 and an
impedance 31 that is connected in parallel with the antenna 32.
Again, the impedance 31 can be switched in series to the antenna
32. The impedance 31 is used for matching an antenna impedance to
an output impedance of the power amplifier 28 in order to achieve a
maximum power transfer from the power amplifier 28 to the antenna
32.
[0040] A second output of the power amplifier 28 is connected to an
analog-digital converter 29. A voltage from the last stage of the
power amplifier 28 is transferred to the analog-digital converter
29. The voltage is characteristic for the actual output power of
the power amplifier 28. The analog-digital converter 29 converts
this test voltage to a digital signal that is transferred to the
processor 30. The processor 30 calculates for this test signal an
optimum impedance for the impedance 31 and transfers an according
signal to the impedance 31. Furthermore, the processor 30 is
connected by a second output to the power amplifier 28 to send a
control signal to the power amplifier 28. Attached to the impedance
31 is a signal processing unit that is used to set a variable
reactance of the impedance 31, so that a matching to the output
impedance of the amplifier 28 is achieved.
[0041] In FIG. 4, a circuit diagram of the impedance 31 is shown.
This circuit diagram is also valid for the impedances 11 and 23. A
signal processing unit 34 receives a signal 33 from the processor
30. According to this signal 33, the signal processing unit 34
operates switches that connect inductors and capacitors being
switched in parallel. The signal processing unit 34 is therefore
connected to a switch 54 and to switches 56, 58, 60, 45, 47, 49 and
51. The signal processing unit 34 opens and closes those
switches.
[0042] The switches 54, 56, 58 and 60 connect inductors switched in
parallel together. An inductor 53 is connected to a ground and on
the other side to the switch 54 and an output 62 which is connected
to the output of the amplifier 28 and the antenna 32. The switch 54
is on the other side connected to an inductor 55 that is also
connected to the switch 56. The inductor 55 is on the other side
connected to a ground. The switch 56 is on the other side connected
to an inductor 57 and a switch 58. The inductor 57 is connected on
the other side to a ground. The switch 58 is connected on the other
side to an inductor 59 and the switch 60. The inductor 59 is
connected on the other side to a ground. The switch 60 is connected
on the other side to a ground.
[0043] To embody the inductors in integrated circuits, an inductor
is replaced by a circuit made of other circuit elements like
resistors, operational amplifiers and capacitors. In FIG. 5, such a
circuit is presented. An input 70 of the circuit is connected to a
capacitor 71 and to a resistor 74. The capacitor 71 is on its other
side connected to a resistor 72 which is connected itself to a
ground and to a resistor 73 which is then connected to a positive
input of an operational amplifier 75. Mircostrip lines are an
alternative; they are explained below.
[0044] The resistor 75 is connected on its other side to the
negative input of the operational amplifier 75 and to the output of
the operational amplifier 75. From the input 70, an inductance
which is determined by the value of the capacitor 71, the resistor
72, 73, and 74 and the operational amplifier 75.
[0045] The switches 45, 47, 49, and 51 are used to switch
capacitors together in parallel. The capacitor 44 is on one side
connected to a ground and on the other side connected to the switch
45 and to the output 62. The switch 45 is connected on the other
side to a capacitor 46 and a switch 47. The capacitor 46 is
connected on the other side to a ground. The switch 47 is connected
on the other side to the capacitor 48 and to the switch 49. The
capacitor 48 is connected on the other side to a ground. The switch
49 is connected on the other side to the capacitor 50 and to the
switch 51. The capacitor 50 is connected on the other side to a
ground. The switch 51 is connected on the other side to a
ground.
[0046] By switching together these inductors and capacitors,
several values for a reactance of the impedance 31 are realized.
The number of possible reactances can be increased by switching
together more capacitors and more inductors together.
Alternatively, one can realize the inductors and capacitors by
variable inductors and capacitors. Then, a signal processing unit
applies directly a signal to the capacitors and conductors in order
to change respectively the capacitance and inductance of these
circuit elements.
[0047] Apart from realizing the impedance with the variable
reactance separate from the antenna, the variable reactance can be
integrated in the antenna. For mobile phones, patch antennas are
widely used. A patch antenna includes a metal plate deposited on a
dielectric layer. The dielectric layer is either a substrate itself
or it is deposited on another substrate, for example on a
semiconductor substrate on which the electronics is fabricated. A
feed line to the patch antenna is either buried below the
dielectric layer using electromagnetic coupling for transferring
the signals from the feed line to the patch antenna or the feed
line is a microstrip line in vicinity to the antenna also using
electromagnetic coupling or the feed line is directly connected to
the patch antenna or the feed line consists of a slot through the
dielectric layer thereby providing a waveguide.
[0048] In FIG. 6, a patch antenna with a variable reactance is
shown. A metal plate 70 as the patch antenna is fed by a line 71
connecting the patch antenna 70 and a transmitter with the power
amplifier and a receiver. Thus, the antenna 70 receives the signals
to be transmitted by the line 71.
[0049] Furthermore, a shortening pin (not shown) is connected to
the antenna 70. The shortening pin is connected to a switch 72 and
a capacitor 73, which are grounded. By opening and closing the
switch, the reactance of the antenna 70 is changed. By adding more
capacitors and switches, more values for the reactance can be
realized. The shortening pin 83 exhibits an inductance. The switch
72 is either operated by an attached signal processing unit that is
connected to a processor described above or by the processor
itself. The shortening pin 83 passes through the dielectric
layer.
[0050] In FIG. 7, another embodiment of realizing the variable
reactance is shown. A metal plate 74 acting as an antenna is fed by
a line 75. A shortening pin 76 as an inductor connects the metal
plate 74 to a ground whereas another shortening pin 84 as an
additional inductor connects the metal plate 74 to a switch 77
which connects the shortening pin 84 to a ground. By opening and
closing the switch 77 the inductance of the antenna is changed. By
adding more shortening pins more inductance values can be realized.
In combination with the capacitors switched to the metal plate 74
as shown in FIG. 6, using these shortening pins with switches an
even wider range of reactance values can be realized. For the
operation of the switch 77, the same is valid as mentioned for FIG.
6.
[0051] In FIG. 8, another embodiment of realizing the variable
reactance is shown. A metal plate 78 acting as an antenna is fed by
a line 80 with the signals to be transmitted. A shortening pin 79
connects the metal plate to a ground and provides an inductance. A
capacitor 81 connects the metal plate 78 to a switch 82 that is
itself connected to a ground. By opening and closing the switch 82,
a variable capacitance and thereby a variable reactance is
realized. Adding more capacitors with switches extends the range of
possible reactances. By combining this realization with those
presented in FIG. 6 and FIG. 7, a very large range of possible
reactances can be realized. A further extension is possible by
adding capacitors with variable capacitances. For the operation of
the switch 82, the same is valid as mentioned for FIG. 6.
[0052] Reactances can also be realized by microstrip lines. Due to
length of a microstrip line, it transforms an open end of the
microstrip line or a shortcut to any reactance, so that capacitors
and inductors can be replaced. In microwave engineering, a length
of a transmission line is no longer much smaller than a wavelength
of a signal, so that an individual length of a transmission line
determines which phase and amplitude of the signal is at the end of
the transmission line, so that depending on the length of the
transmission line you see once an inductance or a capacitance at
the end of the transmission line.
[0053] A microstrip line is a transmission line including a
metallized strip and a solid ground plane metallization separated
by a thin, solid dielectric. This transmission line configuration
is used since it permits accurate fabrication of transmission line
elements on a ceramic substrate.
[0054] The processor stores the calculated impedance setting for
each measured value thereby creating a table putting measured
values in relation to the calculated impedance settings. Next time,
when again a value is measured that is stored in the table, then
the processor does not need to perform calculations again but it
takes only the previously calculated value out of the table and
transmits it to the impedance. When there are enough values in the
table, the processor can start to interpolate for newly measured
values that are between to previously measured values in order to
save processing time and storage capacity.
[0055] In addition, the processor stores the actual value of the
impedance, so that if the measurement leads to the same value, the
processor will not transmit a signal to the impedance.
* * * * *